The invention relates to fuel systems for compressed natural gas fuelled (CNG) vehicles or the like. In particular, the invention relates to a solenoid assembly to control the flow of fuel for a CNG fuelled vehicle or the like.
When compressed natural gas (CNG) is used to fuel vehicles, it is stored in thick walled cylinders at pressures as high as 4500 psig. As there is no fuel pump, an electrical solenoid is used to start and stop the flow of CNG from the cylinders to the engine""s fuelling system. In order to ensure that the vehicle can be quickly re-fuelled, and that it can operate at low cylinder pressures, such solenoids require large orifices. Orifices of 0.150-0.250xe2x80x3 are common. Notably, at 4500 psig, 220 lbs. of force would be required to open a 0.250xe2x80x3 orifice solenoid. Such a force is beyond the capability of reasonably sized 12 Vdc direct acting solenoids.
Accordingly, pilot operated solenoids are used. Such solenoids have a direct acting portion (the pilot stage) which opens a small orifice (typically 0.015-0.030xe2x80x3 diameter). That small orifice supplies pressure (flow) to the downstream system. Once the pilot flow has nearly equalized the upstream and downstream pressures, a large (primary) stage opens. The primary stage would have the 0.150xe2x80x3-0.250xe2x80x3 diameter orifice. Both mechanical and pneumatic means are used to couple the pilot and primary stages. Such schemes require large, expensive solenoid coils, generating a significant amount of heat. Further, they are slow to open the primary stage at low cylinder pressures, causing driver complaints (engine won""t accept throttle).
Ideally, such solenoids would open instantly (e.g. in less than 250 milliseconds). Further, they would be installed inside the neck of the thick walled cylinder. Such xe2x80x9cinternalxe2x80x9d installation would protect them from physical abuse (both normally and in crashes) and would also protect them from environmental insult (salt spray, stone toss). However, most current solenoids are too large to fit within the neck of common cylinders. (Note: common cylinders neck openings may be as small as 0.840xe2x80x3).
Ideally such solenoids would be able to accommodate the two common flow configurations chosen by vehicle designers. One scheme, Configuration 1, has the solenoid""s inlet connected to the gas inside the master cylinder. In that case, the master cylinder is refueled through the solenoid, and its primary piston acts as a back check valve.
In Configuration 2 the solenoid is supplied from an external manifold (fuel rail) which is common to all of the on-board storage cylinders. In that case, even though the solenoid would be installed inside one cylinder (e.g. the master cylinder) its inlet would be isolated from the gas in that cylinder. That is, its inlet would be connected to the external fuel rail. In that case, the master cylinder would not be fueled through the solenoid. Most common solenoids cannot accommodate both of these configurations.
Most common solenoids use rubber orifice seals, which are prone to manufacturing quality problems and to reliability problems in service. When solenoids are placed inside cylinders, the coil leads can be effected by the gas fill blast (high velocity and as cold as xe2x88x92190xc2x0 F.). Ideally the coil wires would be shielded from the gas blast and/or routed so that the gas blast misses them. Further, many common solenoids place the primary sealing surface such that the fill-gas impinges directly onto the elastomer face. This condition reduces both the life expectancy and the reliability of those solenoids.
This invention provides an electrically operated, pilot-type, xe2x80x9cinstant-onxe2x80x9d solenoid addressing all of the issues mentioned above. The advantages of this invention include but are not limited to the following:
This invention is also simple in design and does not require expensive tooling.
In its first form, the invention operates from the gas inside the master cylinder and acts as a re-fuelling check valve. In a second embodiment, the invention is slightly modified to be installed inside a cylinder, while operating from an external fuel rail.